Downhole fluids with a particular impedance

ABSTRACT

The present disclosure relates to a composite fluid including a foundation fluid having an impedance at a frequency, and an additive combined with the foundation fluid that results in a composite fluid having an impedance different than the impedance of the foundation fluid at the frequency.

TECHNICAL FIELD

The present disclosure relates to downhole fluids and, moreparticularly, downhole fluids with a high dielectric constant and a highdielectric strength.

BACKGROUND

Natural resources, such as oil or gas, residing in a subterraneanformation can be recovered by drilling a wellbore that penetrates theformation. A variety of fluids are used in both drilling and completingthe wellbore and in resource recovery. Each of these fluids may servedifferent purposes within a wellbore. During the drilling of thewellbore, for example, a drilling fluid may be used to, among otherthings, cool the drill bit, lubricate the rotating drill string toprevent it from sticking to the walls of the wellbore, prevent blowoutsby serving as a hydrostatic head to the entrance into the wellbore offormation fluids, and remove drill cuttings from the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the various embodimentsand advantages thereof may be acquired by referring to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features, and wherein:

FIG. 1 is an elevation view of an exemplary drilling system in which adrilling fluid may be used;

FIG. 2 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of particles inthe composite fluid for varying conductivities of the composite fluid;

FIG. 3 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of particles withvarying electric dipole moments per unit volume; and

FIG. 4 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying dielectric constants;

FIG. 5 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles withvarying dielectric constants;

FIG. 6 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying conductivities;

FIG. 7 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles withvarying conductivities;

FIG. 8 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles in the composite fluid for varying conductivities of thecomposite fluid;

FIG. 9 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles inthe composite fluid for varying conductivities of the foundation fluid;

FIG. 10 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the operating frequency of theelectric potential or field;

FIG. 11 is a graph illustrating the relationship between the effectiveconductivity of the composite fluid and the volume fraction of additiveparticles with varying operating frequencies of the electric potential;

FIG. 12 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying dielectric constants enhanced by increasing theelectric dipole moment per unit volume of the additive particles; and

FIG. 13 is an elevation view of an exemplary wellbore in which a spacerfluid may be used.

DETAILED DESCRIPTION

A downhole fluid with particular electrical and/or magnetic propertiesmay be formulated by combining a foundation fluid with particles and/orother fluids, which may be collectively referred to as “additives,” toform a composite fluid with electrical and/or magnetic propertiesdifferent from those of the foundation fluid. The particular electricaland/or magnetic properties of the downhole fluid may be formulated toachieve or maintain a particular environment within the wellbore duringdrilling, completion, maintenance, or operation of a well. Theelectrical and/or magnetic properties of the downhole fluids may affecthow system components within the wellbore interact with one another, thewellbore, and the surrounding formation. As an example, the electricalproperties of the downhole fluid may, among other things, affect theflow of electrical current through the downhole fluid. As anotherexample, the magnetic properties of a downhole fluid may, among otherthings, affect how system components magnetically attract, repulse, orotherwise influence one another. Thus, additives may be used toformulate a downhole fluid with particular electrical and/or magneticproperties in order to achieve or maintain a particular environmentwithin the wellbore. Embodiments of the present disclosure and itsadvantages may be understood by referring to FIGS. 1 through 4, wherelike numbers are used to indicate like and corresponding parts.

FIG. 1 is an elevation view of an exemplary drilling system in which adrilling fluid may be used. Drilling system 100 may include drillingplatform 102 that supports derrick 104 having traveling block 106 forraising and lowering drill string 108. Kelly 110 may support drillstring 108 as it is lowered through rotary table 112. Drill bit 114 maybe attached to the distal end of drill string 108 and may be driveneither by a downhole motor and/or via rotation of drill string 108 fromthe well surface. As drill hit 114 rotates, it may create wellbore 116,which penetrates various subterranean formations 118. Wellbore 116 maybe any hole drilled into a formation for the purpose of exploration orextraction of natural resources such as, for example, hydrocarbons, orfor the purpose of injection of fluids such as, for example, water,wastewater, brine, or water mixed with other fluids. Additionally,wellbore 116 may be any hole drilled into a formation for the purpose ofgeothermal power generation.

Drilling system 100 may also include pump 120, which circulates drillingfluid 122 through feed pipe 124 to kelly 110, which in turn conveysdrilling fluid 122 downhole through the interior of drill string 108 andthrough one or more orifices in drill bit 114. Drilling fluid 122 maythen circulate back to the surface via annulus 126 formed between drillstring 108 and the sidewalls of wellbore 116. At the surface,recirculated or spent drilling fluid 122 may exit annulus 126 and may beconveyed to one or more fluid processing units 128 via aninterconnecting flow line 130. After passing through fluid processingunits 128, a cleaned drilling fluid 122 may be deposited into retentionpit 132. Although fluid processing unit 128 is illustrated in FIG. 1near the outlet of the wellbore 116, fluid processing unit 128 may belocated at a distance from the outlet of well bore 116.

Drilling system 100 may further include mixing hopper 134 communicablycoupled to or otherwise in fluidic communication with retention pit 132.Mixing hopper 134 may include, but is not limited to, mixers and relatedmixing equipment. Mixing hopper 134 may be used to add additives todrilling fluid 122 to create a composite fluid.

Additives may be used to create drilling fluid 122 with specificelectrical and/or magnetic properties. Drilling fluid 122 may be acomposite fluid including a foundation fluid to which particles and/orother fluids, which may collectively be referred to as additives, areadded to create a new composite fluid with magnetic and/or electricalproperties different than those of the foundation fluid. The electricaland/or magnetic properties of drilling fluid 122 may be selected oradjusted with additives based on the intended use of drilling fluid 122within the wellbore and/or the actual or anticipated conditions withinthe wellbore during drilling, completion, maintenance, or operation ofthe well.

A downhole fluid may be any fluid used in the drilling, completion,maintenance, or operation of a well. For example, in addition todrilling fluid 122 described in FIG. 1, other downhole fluids, such asspacer fluids and fracturing fluids, may be similarly composed of afoundation fluid to which additives including particles and/or otherfluids are added. Spacer fluids and fracturing fluids may be used inplace of drilling fluid 122 in drilling system 100 or another drillingsystem or well system as appropriate. As another example, the downholefluid may be concrete to which additives including particles and/orother fluids are added prior to the concrete completely curing.

This disclosure describes techniques for modifying the electrical andmagnetic properties of a downhole fluid (e.g., drilling fluid 122,spacer fluids, fracturing fluids, concrete, or other fluids useddownhole), as well as techniques for using the resulting fluid forimpedance matching. As an example, additives may be selected and addedto change the electrical properties of the downhole fluid. As anotherexample, additives may be selected and added to change the magneticproperties of the fluid. As yet another example, additives may beselected and added to change the electrical and magnetic properties ofthe fluid. The additives may be selected and added to change theelectrical and/or magnetic properties of the fluid for the purpose ofimpedance matching.

Electrical Properties

A downhole fluid may be formulated or modified to have particularelectrical properties in order to limit electrical discharge through thedownhole fluid. In electric discharge drilling, for example, a lowfrequency, high electric field may be applied to a targeted region offormation 118, which may cause formation 118 to physically break downaround the targeted region. To limit discharge of the electric fieldthrough the downhole fluid and allow more electrical current to flowinto the targeted region of formation 118, an electrically insulatingdownhole fluid with a high dielectric constant and a high dielectricstrength at a particular operating frequency may be used. Anelectrically insulating downhole fluid may restrict the movement ofelectrical charges, and therefore, the flow of electrical currentthrough the downhole fluid. A high dielectric constant and highdielectric strength may also decrease electrical discharge through thedownhole fluid. The dielectric constant of the downhole fluid mayindicate the ability of the downhole fluid to store electrical energywhen exposed to an electric field, such as a voltage potential createdby an electric discharge drilling system, while the dielectric strengthof the downhole fluid may indicate a voltage level to which the downholefluid may be exposed before experiencing electrical breakdown, or a lossof its electrically insulating properties. The foundation fluid may bean electrically insulating fluid. The foundation fluid may include asingle fluid or a combination of more than one fluid. The components ofthe foundation fluid may be synthetically produced or refined fromnaturally occurring materials with electrically insulating properties.Further, the components of the foundation fluid may be selected towithstand a range of temperatures and pressures typical within awellbore. For example, non-aqueous, oil-based fluids may withstandhigher temperatures and higher pressures before breaking down ascompared to other aqueous fluids. As an example, the foundation fluidmay be formed of compounds including branched-chain paraffins havingbetween approximately 18 and 40 carbon atoms per molecule, diester oils,hydrocarbon liquids substantially immiscible with water, oleaginousfluids (e.g., esters, olefins, diesel oils, and mineral oils includingn-paraffins, iso-paraffins, cyclic alkanes, and/or branched alkanes),low polynuclear aromatic oils with a mixture of branched and cyclicparaffins, asphaltic mineral oils, and/or asphaltic residual fuel oils,and combinations thereof.

One or more additives may be selected to add to the foundation fluid toform a composite fluid with different electrical properties than thoseof the foundation fluid. Additives may be selected such that, whencombined with the foundation fluid, the addition of additives results inthe formation of a composite fluid with a dielectric constant and/ordielectric strength approximately equal to a target value or within atarget range. The target value or range may be different from the valueor range of the dielectric constant and/or dielectric strength of thefoundation fluid. For example, one or more additives may be selectedsuch that, when added to the foundation fluid, the addition of theadditives results in the formation of a composite fluid with adielectric constant and/or dielectric strength greater than thedielectric constant and/or dielectric strength of the foundation fluid.Additionally, one or more additives may be selected such that, whenadded to the foundation fluid or composite fluid, the addition of theadditives results in the formation of a composite fluid with adielectric constant and/or dielectric strength less than the dielectricconstant and/or dielectric strength of the foundation fluid.

Additives may include particles, fluids, and combinations thereof. Forexample, an additive may include particles formed of a compositionhaving a dielectric constant and/or a dielectric strength greater thanthat of the foundation fluid. As another example, additives may beformed of a mixture of different particles where each type of particleis formed of a composition having a dielectric constant and/or adielectric strength greater than that of the foundation fluid. Additivesmay also include one or more fluids. For example, the additive mayinclude a fluid having a conductivity greater than that of thefoundation fluid. As another example, the additive may includeadditional foundation fluid.

Adding additives to the foundation fluid may form a composite fluid withdifferent electrical properties than those of the foundation fluid. Asan example, the addition to the foundation fluid of particles with adielectric constant greater than that of the foundation fluid may resultin the formation of a composite fluid with a dielectric constant greaterthan that of the foundation fluid. As another example, the addition tothe foundation fluid of particles with a dielectric strength greaterthan that of the foundation fluid may result in the formation of acomposite fluid with a dielectric strength greater than that of thefoundation fluid. Further, the addition to the foundation fluid ofparticles with both a dielectric constant and a dielectric strengthgreater than those of the foundation fluid may result in the formationof a composite fluid with a dielectric constant and a dielectricstrength greater than those of the foundation fluid. In order tomaximize the dielectric constant of the composite fluid, the particlesmay be treated to have electric dipole moments, the particles may becreated with electric dipole moments, and/or the conductivity of thefoundation fluid may be increased according to the methods described inmore detail below.

The electrical conductivity of the particles may also affect thedielectric constant and dielectric strength of the composite fluidformed through the addition of the particles to the foundation fluid.For example, as the electrical conductivity of the particles increases,the enhancement to the dielectric constant and/or the dielectricstrength of the composite fluid may diminish. Thus, the particles may beformed of a composition with an electrical conductivity less than thatof the foundation fluid to provide a greater enhancement to thedielectric constant and/or dielectric strength of the composite fluid.As an example, the particles may be formed of a composition having anelectrical conductivity of approximately one half the electricalconductivity of the foundation fluid.

Exemplary compositions from which the particles may be formed includemica in any of its various forms (e.g., muscovite, phlogopite,leidolite, fluorophlogopite, glass-bonded mica, and biotite),polytetrafluoroethylene (Teflon® by DuPont Co.) and/or chemical variantsof tetrafluoroethylene, glass or a composition of glass including fusedsilica and alkali-silicate, polystyrene, polyethylene, diamond, leadzirconate titanate (PTO, sodium chloride crystalline, potassium bromidecrystalline, silicone oil, benzene, and combinations thereof.

Additionally, the particles may be formed of other compositions having adielectric constant between approximately 2 and 100, and a dielectricstrength of between approximately 10 and 200 kilovolts per mm (kV/mm).

The shape of the particles may be selected based on the target value orrange of the dielectric constant and/or dielectric strength of thecomposite fluid as compared to the foundation fluid. For example, theaddition of particles in the shape of disks or flakes may result in agreater increase in the dielectric constant and/or dielectric strengthof the composite fluid than the addition of particles in the shape ofneedles, ellipsoids, and spheres. The size of the particles may beselected to be larger than the chemical compounds of the material(s)from which the particles are formed, yet small enough to ensure uniformdistribution within the composite fluid. For example, particles in theshape of flakes with a diameter between approximately 10 nm and 100,000nm may uniformly distribute into the composite fluid such that allportions of composite fluid maintain a relatively uniform dielectricconstant and dielectric strength. As an example, the particles may bedisks with a diameter of approximately 50 nanometers (nm) and athickness of approximately 2 nm.

An additive may also include particles that, when added to thefoundation fluid result in the formation of a composite fluid with anincreased electric dipole moment per unit volume, and thus a dielectricconstant greater than the foundation fluid. The average electric dipolemoment per unit volume, which may also be referred to as thepolarization density of a composition, may represent the number andstrength of electric dipoles in the composition. The electric dipoles inthe particles may increase the available electrical polarizationmechanisms in the composite fluid to which the particles are added.Thus, when an external electric field is applied to the composite fluid,the electric dipoles in the particles, and thus in the composite fluid,may align to oppose the external electric field. The alignment of theelectric dipoles in opposition of the external electric field may resultin a higher net electrical polarization in the composite fluid ascompared to the foundation fluid. As discussed in more detail withrespect to FIG. 3, increases in the polarization density of thecomposite fluid may cause increases in the dielectric constant of thecomposite fluid.

Particles may be treated to have electric dipoles and/or created to havea net electric dipole moment.

Particles may be treated to impart electric dipoles within thecomposition from which the particles are formed. For example, theparticles may be placed in the presence of an electric field that causesthe formation of electric dipoles within the composition from which theparticles are formed and, while in the presence of the electric field,heated to a temperature beyond the melting point of the composition fromwhich the particles are formed and subsequently cooled. Heating andcooling the particles while in the presence of the electric field mayresult in the creation of electric dipoles that continue after theparticles are removed from the electric field. The electric dipoles maybe quasi-permanent, which may be referred to as electrets, or permanent,which may be referred to as permanent electric dipoles. The formation ofquasi-permanent and permanent electric dipoles in a particle mayincrease the electric dipole moment per unit volume in the particle. Theresulting electric dipole moment per unit volume for a particularparticle may depend on the magnitude and number of electric dipolescreated by the treatment of the particle. The magnitude and number ofelectric dipoles created by the treatment of a particle may depend on,among other things, the magnitude of the electric field to which theparticle is exposed, the duration of exposure, the temperature to whichthe particle is heated, and the molecular structure of the compositionfrom which the particle is formed.

In addition to treating particles to impart electric dipoles, particlesmay be created to have a net electric dipole moment. Such particles may,for example, include Janus particles created with a net electric dipolemoment. A Janus particle may include a spherical or ellipsoidal particleincluding two distinct regions. The two regions may have differentelectrical polarities, creating net electric dipole moment for theparticle. Particles having a net electric dipole moment may be createdby thermal evaporation, masking, emulsions, site-specific growth, or anyother method that allows for the creation of a two-sided particle withdifferent electrical polarities. The dipole moment of Janus particlesmay be further enhanced by placing the particles in the presence of anelectric field and, while in the presence of the electric field, heatingthe particles to a temperature beyond the melting point of thecomposition from which the particles are formed. The particles createdto have net electric dipole moments may be combined with the foundationfluid to form a composite fluid with a dielectric constant greater thanthat of the foundation fluid.

Particles treated to have electric dipoles and/or particles created tohave a net electric dipole moment may be formed of any compositioncapable of electrical polarization. Exemplary compositions of particlesthat may be treated to impart an electric dipole include mica in any ofits various forms, polytetrafluoroethylene, chemical variants oftetrafluoroethylene, glass, polystyrene, polyethylene, diamond, leadzirconate titanate (PZT), sodium chloride crystalline, potassium bromidecrystalline, silicone oil, benzene, and combinations thereof.

The size and shape of particles treated to impart or created withelectric dipoles may be selected to ensure uniform distribution withinthe composite fluid. For example, particles in the shape of flakes witha diameter between approximately 10 nm and 100,000 nm may uniformlydistribute into the composite fluid such that the composite fluid has arelatively uniform dielectric constant. As the size of the particlesincreases, the distribution of the particles within the composite fluidmay vary, which may cause variation in the dielectric constantthroughout the composite fluid.

As another example, an additive may include a conductive fluid that issoluble in the foundation fluid. The addition to the foundation fluid ofa conductive fluid that is soluble in the foundation fluid may result inthe formation of a composite fluid with an electrical conductivitygreater than that of the foundation fluid. A composite fluid with agreater conductivity than that of the foundation fluid, when combinedwith particles having a dielectric constant greater than that of thefoundation fluid combined with the conductive fluid, may result in adielectric constant much greater than would occur from adding theparticles alone. As discussed in more detail with respect to FIG. 2,increasing the conductivity of the composite fluid may result in greaterenhancement of the dielectric constant of the resulting composite fluidthan would be achieved through the addition of particles alone.

The conductive fluid may be formed of a composition having an electricalconductivity greater than that of the foundation fluid. Exemplarycompositions from which the conductive fluid may be formed include analcohol or a derivative thereof (such as glycol, ethylene glycol,butylene glycol, propylene glycol, pentylene glycol, hexamethyleneglycol, heptamethylene glycol, octamethylene glycol, monoethylene glycoldiethylene glycol, triethylene glycol, tetraethylene glycol, methylalcohol, benzyl alcohol, diethyl oxylate, and/or ethyle amine),guaiacol, methyl acetate, ethyl acetate, butyl acetate, and combinationsthereof.

As yet another example, an additive may include foundation fluid. Forexample, if the dielectric constant and/or dielectric strength of theresulting composite fluid exceeds the target value or range followingthe addition of one or more additives, additional foundation fluid maybe added to dilute the composite fluid and thus reduce the dielectricconstant and/or dielectric strength of the composite fluid.

Analytical estimates may be used to select the additive(s) added to thefoundation fluid in order to form a composite fluid with a dielectricconstant and/or dielectric strength approximately equal to a targetvalue or within a target range. These methods may take into account theproperties of the additive(s) (e.g., dielectric constant, dielectricstrength, and/or conductivity), the properties of the foundation fluid(e.g., dielectric constant, dielectric strength, and/or conductivity),and the properties of any other components in the composite fluid.Analytical estimates may also take into account conditions in which thecomposite fluid will be used and what effect those conditions will haveon the composite fluid. For example, the dielectric constant and/ordielectric strength of the composite fluid may change based on thefrequency of the electric fields exerted on the fluid and/or thetemperature of the fluid. If the dielectric constant and/or thedielectric strength of the resulting composite fluid are notapproximately equal to the target value or within the target range, thenadditional additives may be selected and added to the fluid.

The additives may be added to the foundation fluid to form a compositefluid with electrical properties different than those of the foundationfluid. The amount of an additive to be added to the foundation fluid maybe selected such that the combination of the additive and the foundationfluid results in the formation of a composite fluid with a dielectricconstant and/or dielectric strength approximately equal to a targetvalue or within a target range. The amount of an additive added to thefoundation fluid may affect the dielectric constant and/or dielectricstrength of the resulting composite fluid. For example, increasing theamount of additive added to the foundation fluid may result in anincrease in the dielectric constant and/or dielectric strength of theresulting composite fluid. The amount of an additive necessary to form acomposite fluid with a dielectric constant and/or dielectric strengthapproximately equal to the target value or within the target range mayvary depending on, for example, the volume fraction of the additive, thedielectric constant and/or dielectric strength of the additive andfoundation fluid, the electrical conductivity of the additive andfoundation fluid, and/or the conditions within the wellbore. Exemplaryeffects of additives on the electrical properties of a downhole fluidare discussed in further detail with respect to FIGS. 2 and 3.

Additives may be added to the foundation fluid at the well site or maybe added to the foundation fluid before the foundation fluid is broughtto the well site. For example, additives may be added to the foundationfluid via mixing hopper 134 (shown in FIG. 1) before the fluid is pumpedinto the wellbore. As another example, additives may added to acontainer in which the foundation fluid is stored (e.g., retention pit132 shown in FIG. 1) such that the additives are mixed into thefoundation fluid as the fluid is pumped into the wellbore. As yetanother example, the additives may be placed into the wellbore and mixedwith the foundation fluid as the fluid circulates within the wellbore.As still another example, additives may be added to the foundation fluidduring the manufacture and/or preparation of the composite fluid.

FIG. 2 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of particles inthe composite fluid for varying conductivities of the composite fluid.Each of plots 202, 208, 214, and 220 represents a composite fluid with adifferent level of electrical conductivity. For example, plot 202 mayrepresent the relationship between the dielectric constant of acomposite fluid and the volume fraction of particles in the compositefluid where the conductivity of the composite fluid has not beenincreased through the addition of a conductive fluid to the foundationfluid. As illustrated by plot 202, the dielectric constant of thecomposite fluid may increase monotonically as the volume fraction ofparticles increases to volume fraction 204. The addition of particlesbeyond volume fraction 204, however, may result in a relative decreasein the dielectric constant of the composite fluid. Dielectric constant206 may represent the maximum achievable dielectric constant for acomposite fluid with the particular combination of foundation fluid andadditives represented by plot 202. As illustrated later in FIG. 8, anyincrease in the dielectric constant of the composite fluid caused byincreasing the Active 18295314.3 volume fraction of particles maydiminish with less conductive foundation fluids (e.g., 1e⁻⁰⁹ mhos permeter).

Increasing the conductivity of the composite fluid through the additionof a conductive fluid to the foundation fluid may result in greaterenhancement of the dielectric constant of the resulting composite fluidthan would be achieved through the addition of particles alone. Forexample, plot 208 may represent the relationship between the dielectricconstant of a composite fluid and the volume fraction of particles inthe composite fluid where the conductivity of the composite fluid hasbeen increased, relative to the fluid represented by plot 202, throughthe addition of a conductive fluid to the foundation fluid. Compared toplot 202, in which the fluid has a lower conductivity, plot 208illustrates that, when the conductivity of the composite fluid isincreased, a higher dielectric constant may be achieved withoutincreasing the volume fraction of particles in the composite fluid. Apeak in plot 208 at dielectric constant 212 may occur at volume fraction210, representing the maximum dielectric constant for a composite fluidwith the particular combination of foundation fluid and additivesrepresented by plot 208. The maximum dielectric constant for plot 208may be higher than the maximum dielectric constant for plot 202, and thepeak in plot 208 may occur at a lower volume fraction of particles inthe composite fluid compared to plot 202. This may be due at least inpart to the increased conductivity of the fluid represented by plot 208.Thus, increasing the conductivity of the composite fluid may result in agreater enhancement of the dielectric constant for the composite fluidat a lower volume fraction of particles.

The relative increase in the dielectric constant of the composite fluidmay, however, diminish as the conductivity of the fluid continues toincrease. For example, plots 214 and 220 may represent composite fluidswith conductivity levels greater than the fluids represented by plots202 and 208. As illustrated by plots 214 and 220, the relative increasein the dielectric constant of the fluids represented by plots 214 and220 is less than the relative increase in dielectric constant for thefluids represented by plots 202 and 208. Thus, the relative increase inmaximum dielectric constants may diminish as the conductivity of thecomposite fluid continues to increase.

As illustrated by plots 202, 208, 214, and 220, a variety of techniquesmay be used to form a composite fluid with a desired dielectricconstant. For example, the conductivity of the composite fluid may beincreased through the addition of a conductive fluid to the foundationfluid, particles having a dielectric constant greater than that of thefoundation fluid may be added to the foundation fluid, or a combinationof these techniques may be employed. Different foundation fluids andadditives may exhibit different responses to changes in the conductivityof the fluid and volume fractions of particles.

The decision on whether to increase the conductivity of the foundationfluid and/or add more particles may be based on the properties of theparticular foundation fluid and/or additive(s) used, which may beobtained through analytical estimates, experimentation, or materialspecification sheets for the different materials, the desired propertiesof the composite fluid (e.g., the stability or lubricity of theresulting composite fluid), and/or other considerations, such as thedielectric strength of the composite fluid. For example, unlike thedielectric constant, the dielectric strength of a composite fluid mayexhibit little or no correlation to the conductivity of the foundationfluid. Thus, while adding a conductive fluid to the foundation fluid mayreduce the number of particles required to achieve a particulardielectric constant, the reduced number of particles may result in theformation of a composite fluid with a lower dielectric strength whencompared to a composite fluid formed using only particles to obtain thesame dielectric constant. If some compromise to the dielectric strengthof composite fluid is acceptable (e.g., a reduction in the dielectricbreakdown voltage from 30 kV/min to 10 kV/mm), then a conductive fluidadditive with particles having a greater dielectric constant than thatof the foundation fluid combined with the conductive fluid additive maybe used to enhance the dielectric constant of the resulting compositefluid. If however a composite fluid with a high dielectric strength isdesirable, then the conductivity of the composite fluid may be kept aslow as possible by using particles treated and/or created to haveelectric dipoles to increase the dielectric constant of the compositefluid as described in FIG. 3.

FIG. 3 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of particles withvarying electric dipole moments per unit volume. The particles have agreater dielectric constant than the foundation fluid to which they areadded. Adding particles with a dielectric constant greater than that ofthe foundation fluid may result in a composite fluid with amonotonically greater dielectric constant as a function of volumefraction of particles than that of the foundation fluid. However, thedielectric constant of the composite fluid may be considerably enhancedby treating and/or creating particles to have electric dipoles. In thepresence of an electric field, the electric dipoles in the particles mayalign, increasing the polarity of the composite fluid to which theparticles are added. The increased polarity of the composite fluid mayresult in an increased dielectric constant of the composite fluid. Eachof plots 302, 304, and 306 represent a composite fluid includingparticles with varying electric dipole moments per unit volume.

For example, plot 302 represents a composite fluid including particlesthat have not been treated to impart electric dipoles or created withnet electric dipole moments. As illustrated by plot 302, the dielectricconstant of the composite fluid may increase monotonically as the volumefraction of particles having a dielectric constant greater than that ofthe foundation fluid are added. Even further enhancements to thedielectric constant of the composite fluid may be achieved by treatingand/or creating the particles to have electric dipoles.

Plot 304 represents a composite fluid including particles that have beentreated to impart quasi-permanent electric dipoles. Similar to plot 302,the dielectric constant of the composite fluid may increase as thevolume fraction of the particles increases. When compared to plot 302,however, the dielectric constant of the composite fluid represented byplot 304 is greater for the same volume fraction of particles. This isdue at least in part to the addition of particles treated to impartquasi-permanent electric dipoles. The increased electric dipole momentper unit volume may increase the dielectric constant of the particles,and thus the dielectric constant of the composite fluid to which theparticles are added.

Like plot 304, plot 306 may represent a composite fluid includingparticles that have been treated to impart electric dipoles. Theparticles included in the composite fluid represented by plot 306 may,however, have an electric dipole moment per unit volume greater than theparticles included in the composite fluid represented by plot 304. Asillustrated by comparing plots 302, 304, and 306, increasing theelectric dipole moment per unit volume of the particles included in acomposite fluid may result in a greater enhancement of the dielectricconstant for the composite fluid for the same volume fraction ofparticles. That is, as the electric dipole moment per unit volume of theparticles increases, the dielectric constant of the composite fluid mayalso increase for the same volume fraction of particles.

The decision regarding whether to treat or create particles withelectric dipoles may be based on the properties of the particularfoundation fluid and/or additives used, which may be obtained throughanalytical estimates, experimentation, or material specification sheetsfor the different materials, the desired properties of the compositefluid (e.g., the stability or lubricity of the resulting compositefluid), and/or other considerations, such as the dielectric strength ofthe composite fluid. For example, although increasing the electricdipole moment per unit volume of the particles may reduce the amount ofparticles required to create a composite fluid having a particulardielectric constant, the dielectric strength of the composite fluid mayexhibit little or no correlation to the dipole moment per unit volume ofthe particles. Thus, using fewer particles to obtain the same dielectricconstant in the composite fluid may result in the formation of acomposite fluid with a lower dielectric strength when compared to acomposite fluid formed using only particles to obtain the samedielectric constant.

Electrical Properties Examples

Various analyses were conducted to demonstrate the effect of additiveson the resulting composite fluid. Unless stated otherwise, thefoundation fluid is ethyl amine with a dielectric constant of twice thatof a vacuum and a conductivity of 4×10⁻⁵ mhos per meter, the operatingfrequency of the electric field applied to the composite fluid is 200Hertz, and the additive particles are disk shaped and comprised with aconductivity of 10⁻⁵ mhos per meter in the case of mica. The analyseswere conducted for a limited range of volume fractions of additiveparticles as labeled in the individual figures described below.

FIG. 4 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying dielectric constants. As illustrated, the peak inthe dielectric constant of the composite fluid occurs where the volumefraction of the additive particles is low less than 001) and there islittle variation in the highest obtainable dielectric constant of thecomposite fluid based on the dielectric constant of the additiveparticles. As the dielectric constant of the particles increases, thewidth of the peak corresponding to the dielectric constant of thecomposite fluid increases to spread over a wider range of 0.5 volumefractions of particles. Thus, particles with a greater dielectricconstant may improve the stability of the dielectric constant of thecomposite fluid caused by fluctuations in the volume fractions ofparticles.

FIG. 5 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles withvarying dielectric constants. As illustrated, the effective conductivityof the composite fluid decreases rapidly as the volume fraction ofadditive particles in the composite fluid increases. The dielectricconstant of the additive particles and the change in conductivity of thecomposite fluid may be inversely related. For example, the addition ofparticles with a greater dielectric constant may decrease theconductivity of the composite fluid less than the addition of particleswith a lesser dielectric constant. Thus, the greater the dielectricconstant of the additive particles, the less the additive particlesreduce the conductivity of the composite fluid.

FIG. 6 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying conductivities of the additive particles. Theconductivity of the additive particles (e.g., the conductivity of thecomposition from which the particles are comprised) may have littleeffect on the dielectric constant of the composite fluid. However, asthe conductivity of the additive particles increases to, for example,one half the conductivity of the foundation fluid, any increase to thedielectric constant of the composite fluid caused by the addition of theadditive particles may diminish, even as the volume fraction of theadditive particles is increased. Thus, additive particles with a lowconductivity (e.g., less than one half that of the foundation fluid)should be used in order to achieve a greater enhancement to thedielectric constant of the composite fluid.

FIG. 7 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles withvarying conductivities of the composition from which the particles arecomprised. As the conductivity of the additive particles (e.g., theconductivity of the composition from which the particles are comprised)increases, the conductivity of the composite fluid experiences greaterincreases in conductivity because of the additive particles. ConsideringFIGS. 6 and 7 in combination, it may be desirable to utilize additiveparticles having low conductivities (e.g., less than one half that ofthe foundation fluid) to ensure that the enhanced dielectric constantand the low conductivity of the composite fluid are not adverselyaffected by the conductivity of the additive particles.

FIG. 8 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles in the composite fluid for varying conductivities of thecomposite fluid. The enhancement to the dielectric constant of thecomposite fluid may be greater for the same volume fraction of additiveparticles as the conductivity of the foundation fluid is increased. Asthe conductivity of the foundation fluid is increased, greaterenhancement to the dielectric constant of the composite fluid may beachieved with a lesser volume fraction of additive particles. Thus,increasing the conductivity of the foundation fluid may increase thedielectric constant in the composite fluid. However, as the conductivityof the foundation fluid reaches approximately 0.0005 or 0.001 mhos permeter, the relative enhancement to the dielectric constant of thecomposite fluid ceases with further increases to the conductivity of thefoundation fluid. That is, as the conductivity of the foundation fluidreaches a certain value, further increases to the conductivity of thefoundation fluid may have diminishing effects on the dielectric constantof the composite fluid.

FIG. 9 is a graph illustrating the relationship between the conductivityof a composite fluid and the volume fraction of additive particles inthe composite fluid for varying conductivities of the foundation fluid.Until the conductivity of the foundation fluid is relatively high (e.g.,five or more orders of magnitude greater than the composite fluid), theadditive particles have little effect on the conductivity of theresulting composite fluid. Above this ratio, as the conductivity of thefoundation fluid increases, the volume fraction of additive particlesrequired to decrease the conductivity of the resulting composite fluidalso increases.

FIG. 10 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the operating frequency of theelectric potential or field. The dielectric constant and/or dielectricstrength of the composite fluid may change based on the frequency of theelectric potential or fields exerted on the fluid. For example, as thefrequency of the electric potential applied to the composite fluidincreases, the relative increase to the dielectric constant of thecomposite fluid monotonically decreases. Thus, enhancement to thedielectric constant of the composite fluid may be higher at loweroperating frequencies, and decrease as the frequency of the electricpotential increases.

FIG. 11 is a graph illustrating the relationship between the effectiveconductivity of the composite fluid and the volume fraction of additiveparticles with varying operating frequencies of the electric potential.Similar to the dielectric constant and/or dielectric strength, theconductivity of the composite fluid may vary with the operatingfrequency of the electric potential. The effective conductivity of thecomposite material increases relatively uniformly as the frequency ofthe electric potential increases.

FIG. 12 is a graph illustrating the relationship between the dielectricconstant of a composite fluid and the volume fraction of additiveparticles with varying dielectric constants enhanced by increasing theelectric dipole moment per unit volume of the additive panicles. Thefoundation fluid in FIG. 12 has a relatively low conductivity of 10⁻¹⁰mhos per meter. As the dielectric constant of the additive particles isincreased by, for example, increasing the electric dipole moment perunit volume of the particles, the dielectric constant of the compositefluid to which the particles are added increases as well. As the volumefraction of particles exceeds the plotted 0.01 and approaches 1.0, thedielectric constant of the composite fluid asymptotically approaches thedielectric constant of the additive particles. As the conductivity ofthe composite fluid decreases, the volume fraction of additive particleswill have a diminishing effect on the dielectric constant of thecomposite fluid.

Magnetic Properties

The magnetic properties of a downhole fluid may also affect how systemcomponents located within the wellbore interact with one another, thewellbore, and the surrounding formation. The magnetic properties of adownhole fluid bear many similarities to the electrical propertiesdiscussed above. For example, the magnetic permeability of a downholefluid is the magnetic equivalent of the dielectric constant of thedownhole fluid. Similarly, the magnetic reluctance of a downhole fluidis the magnetic equivalent electrical resistance, or the reciprocal ofelectrical conductivity.

Thus, techniques similar to those described above for creating acomposite fluid with particular electrical properties may be used tocreate a composite fluid with particular magnetic properties.

The downhole fluid may be a composite fluid including a foundation fluidto which particles and/or other fluids, which may collectively bereferred to as “additives,” are added to create a new composite fluidwith magnetic properties different than those of the foundation fluid. Afoundation fluid may be provided as the starting product for theformation of a composite fluid. The foundation fluid has a magneticpermeability, which may represent the density of magnetic flux inresponse to the magnetic field, or the degree of magnetization of thefluid in response to a magnetic field.

The foundation fluid may include a single fluid or a combination of morethan one fluid. The components of the foundation fluid may besynthetically produced or refined from naturally occurring materialswith electrically insulating properties. Further, the components of thefoundation fluid may be selected to withstand a range of temperaturesand pressures typical within a wellbore. For example, non-aqueous,oil-based fluids may withstand higher temperatures and higher pressuresbefore breaking down as compared to other aqueous fluids. As an example,the foundation fluid may be formed of compounds including branched-chainparaffins having between approximately 18 and 40 carbon atoms permolecule, diester oils, hydrocarbon liquids substantially immisciblewith water, oleaginous fluids (e.g., esters, olefins, diesel oils, andmineral oils including n-paraffins, iso-paraffins, cyclic alkanes,and/or branched alkanes), low polynuclear aromatic oils with a mixtureof branched and cyclic paraffins, asphaltic mineral oils, and/orasphaltic residual fuel oils, and combinations thereof.

One or more additives may be selected to add to the foundation fluid toform a composite fluid with different magnetic properties than those ofthe foundation fluid.

Additives may be selected such that, when combined with the foundationfluid, the addition of additives results in the formation of a compositefluid with a magnetic permeability approximately equal to a target valueor within a target range. The target value or range may be differentfrom the value or range of the magnetic permeability of the foundationfluid. For example, one or more additives may be selected to be added tothe foundation fluid to create a composite fluid with a magneticpermeability greater than that of the foundation fluid. One or moreadditives may also be selected to be added to the foundation fluid orcomposite fluid to create a composite fluid with a magnetic permeabilityless than the foundation fluid.

Additives may include particles, fluids, and combinations thereof. Forexample, an additive may include particles formed of a compositionhaving a magnetic permeability greater than that of the foundation fluidor particles with magnetic dipoles. As an example, additives may beformed of a mixture of different particles where each type of particleis formed of a composition having a magnetic permeability greater thanthat of the foundation fluid. As another example, an additive may beformed of particles treated in the presence of a magnetic field and ahigh temperature (e.g., a temperature beyond the melting point of thecomposition from which the particles are formed) to create magneticdipoles in the particles. As yet another example, an additive mayinclude Janus particles created with two regions that are magneticallypolarized. The addition to the foundation fluid of particles with amagnetic permeability greater than that of the foundation fluid and/orparticles treated or created with magnetic dipoles may result in theformation of a composite fluid with a magnetic permeability greater thanthat of the foundation fluid.

Exemplary compositions from which the particles may be formed includemica in any of its various forms containing natural ferritic inclusions,ferrite materials (e.g., manganese-zinc ferrite made of the formM_(a)Zn_((1-a))Fe₂O₄, and nickel-zinc ferrite made of the formNi_(a)Zn_((1-a))Fe₂O₄), and/or particles of magnetic materials, such asiron, nickel, and/or cobalt, and combinations thereof.

The size of the particles may be selected to be larger than the chemicalcompounds of the material(s) from which the particles are formed, yetsmall enough to ensure a random, uniform distribution within thecomposite fluid. For example, particles in the shape of flakes with adiameter between approximately 10 nm and 100,000 nm may uniformlydistribute into the composite fluid such that all portions of compositefluid maintain a relatively uniform magnetic permeability. The particlesmay also be in the shape of needles, ellipsoids, spheres, andcombinations thereof. As the size of the particles increases, thedistribution of the particles within the composite fluid may vary, whichmay cause variations in the magnetic permeability throughout thecomposite fluid.

As another example, an additive may include foundation fluid. Forexample, if the magnetic permeability of a composite fluid becomesgreater than the target value or range following the addition of one ormore additives, additional foundation fluid may be added to dilute thecomposite fluid and thus reduce the magnetic permeability of thecomposite fluid.

Analytical estimates may be used to select the additive(s) added to thefoundation fluid in order form a composite fluid with a magneticpermeability approximately equal to the target value or within thetarget range. These methods may take into account the properties (e.g.,magnetic permeability) of the additive(s) and the foundation fluid, andthe properties of any other components in the composite fluid.Analytical estimates may also take into account conditions in which thecomposite fluid will be used and what effect those conditions will haveon the magnetic properties of the composite fluid. For example, themagnetic permeability of the composite fluid may change based on thefrequency of the magnetic fields exerted on the fluid or the temperatureof the fluid.

The additives may be added to the foundation fluid to form a compositefluid with different magnetic properties than those of the foundationfluid. The amount of an additive to be added to the foundation fluid maybe selected such that the combination of the additive and the foundationfluid result in the formation of a composite fluid with a magneticpermeability approximately equal to a target value or within a targetrange. The amount of an additive added to the foundation fluid mayaffect the magnetic permeability of the resulting composite fluid. Forexample, increasing the amount of an additive added to the foundationfluid may result in an increase in the magnetic permeability of theresulting composite fluid. The amount of an additive necessary to form acomposite fluid with a magnetic permeability approximately equal to thetarget value or within the target range may vary depending on, forexample, the volume fraction of the additive, the magnetic permeabilityof the additive and foundation fluid, the magnetic permeability of theadditive and foundation fluid, and/or the conditions within thewellbore. If the magnetic permeability of the resulting composite fluidis not approximately equal to the target value or within the targetrange, then additional additives may be selected and added to the fluid.

Additives may be added to the foundation fluid at the well site or maybe added to the foundation fluid before the foundation fluid is broughtto the well site. For example, particles may be added to the foundationfluid via mixing hopper 134 (shown in FIG. 1) before the fluid is pumpedinto the wellbore. As another example, particles may added to acontainer in which the foundation fluid is stored (e.g., retention pit132 shown in FIG. 1) such that the additives are mixed into thefoundation fluid as the fluid is pumped into the wellbore. As yetanother example, the additives may be placed into the wellbore and mixedwith the foundation fluid as the fluid circulates within the wellbore.As still another example, additives may be added to the foundation fluidduring the manufacture and/or preparation of the composite fluid.

Impedance Matching with Downhole Fluids

Using the teachings of the present disclosure, a downhole fluid may beformed with any combination of electrical and/or magnetic properties.For example, a downhole fluid may be formulated to have a particulardielectric constant, dielectric strength, electrical conductivity,and/or magnetic permeability. One or more additives may be added to afoundation fluid to create a composite fluid with particular electricaland/or magnetic properties or added to an existing fluid to change theelectrical and/or magnetic properties of the existing fluid. Theadditives may include, for example, a conductive fluid, additionalfoundation fluid, particles having particular electrical and/or magneticproperties, including particles with electric dipoles, and/or particleswith magnetic dipoles, and combinations thereof.

Control of both the electrical and magnetic properties of a fluid may beuseful for, among other things, impedance matching. The impedance of anycomposition may be a function of the capacitance, inductance, and/orresistance of the composition. Capacitance relates to the dielectricconstant of a composition, such that increasing the dielectric constantof the composition may increase its capacitance. Inductance relates tothe magnetic permeability of the composition, such that increasing themagnetic permeability of the composition may increase its inductance.Resistance relates to the conductivity of the composition, such thatincreasing the conductivity of the composition may decrease itsresistance. Thus, the impedance of a fluid may be controlled byadjusting the dielectric constant, magnetic permeability, and/orconductivity of the fluid. To achieve impedance matching, the sourceimpedance may be adjusted to approximately match the load impedance, orvice versa as described in more detail below. Because impedance may varyby frequency, impedance matching may account for the operating frequencyof the electric and magnetic fields within the wellbore.

As an example, in electric discharge drilling, the power transfer of thedrill may be maximized by matching the impedance of the electricdischarge drill bit to the impedance of the formation. Matching theimpedance of the drill bit to the formation may minimize energy loss inthe downhole fluid or electrical signal reflection at high frequencies(e.g., greater than 10 megahertz), and thus maximize the power transferfrom the drill bit to the formation. Maximizing the power transfer fromthe electric discharge drill to the targeted region of the formation mayaffect the efficiency and cost of drilling. A downhole fluid may be incontact or surround system components within the wellbore (including thedrill bit), such that the effective impedance of the system componentsmay be affected by the impedance of the downhole fluid. Thus, thedownhole fluid may be used to change the effective impedance of a systemcomponent serving as a source and/or load of an electrical system.Additives may be used to control the dielectric constant, electricalconductivity, and/or magnetic permeability of the downhole fluid, andthus the effective impedance of the system components, including thedrill bit that the downhole fluid surrounds. Therefore, the additives toa downhole fluid may be used to change the effective impedance of thedrill bit to match the impedance of the formation, thereby matching thesource and load impedances of the electric discharge drilling system.

As another example, the impedance of a downhole fluid may be used tominimize the borehole effect on electromagnetic logging tools operatingwithin the wellbore. Variations in the wellbore may affect the accuracyof measurements made by electromagnetic logging tools (e.g., lateralresistivity tools, induction resistivity tools, propagating waveresistivity tools, pulsed resistivity tools, nuclear magnetic resonancetools, and measurement tools) operating within the wellbore in what iscommonly referred to as the borehole effect. The impedance of thedownhole fluid may be adjusted to approximately match the impedance of aformation surrounding the wellbore to the impedance of the wellbore,thereby reducing the borehole effect and increasing the accuracy ofmeasurements made by electromagnetic logging tools.

The impedance of the downhole fluid may be adjusted over time tomaintain impedance matching. For example, the impedance of the formationsurrounding a wellbore may change as drilling progresses. Differentregions of the formation may contain different fluids, such as oil, gas,and water, dispersed among varying porous formations, such as sandstoneand/or shale. As the content of the formation changes, so may theimpedance of the formation. Monitoring equipment, such aselectromagnetic monitoring sensors, placed at or near the drill bit maybe used to monitor the impedance of the formation. Similarly, cuttingsfrom the formation may be tested at the well surface to determine theimpedance of a region of the formation. Upon detecting impedance changesin the formation, the well operator may add additives to the downholefluid to adjust the impedance of the downhole fluid, to for example,change the effective impedance of the drill bit to match that of theformation in electric discharge drilling or change the effectiveimpedance of the wellbore to match that of the formation forelectromagnetic logging. As the new downhole fluid reaches the drillbit, the effective electrical impedance of the drill bit may adjust tomatch the impedance of the formation. Thus, the downhole fluid may bemodified or reformulated over time to adjust to impedance changes thatmay occur within the drilling system. Maintaining the impedance matchingover time may maximize the power transfer from the electric dischargedrill, improving the efficiency and cost of drilling. Further, managedpressure drilling techniques may be used to maintain more than onedownhole fluid within the same wellbore. Placing different downholefluids within different regions of the same wellbore may allow forhigher precision impedance matching if the impedance of the formationvaries at different regions of the wellbore. As an example, differentdownhole fluids may be placed in the different regions of the wellboreto match the particular impedance of the formation surrounding theregion of the wellbore where the fluid is located.

Uses and Delivery Methods for Downhole Fluids

Drilling Fluid

As disclosed in FIG. 1, drilling fluids, including those formulatedand/or modified according to the teachings of the present disclosure,may be used in drilling a wellbore. A drill bit may be mounted on theend of a drill string that may include several sections of drill pipe.The drill bit may be used to extend the wellbore, for example, by theapplication of force and torque to the drill bit. The drilling fluid maybe circulated downwardly through the drill pipe, through the drill bit,and upwardly through the annulus between the drill pipe and theformation to the surface. Other methods of circulation are possible. Thedrilling fluid may be employed for general drilling of a wellbore insubterranean formations, for example, through non-producing zones aswell as for drilling through hydrocarbon-bearing producing zones. Thedrilling fluids may directly or indirectly affect one or more componentsor pieces of equipment associated with the preparation, delivery,recapture, recycling, reuse, and/or disposal of the disclosed drillingfluid. For example, the disclosed drilling fluid may directly orindirectly affect one or more mixers, related mixing equipment, mudpits, storage facilities or units, composition separators, heatexchangers, sensors, gauges, pumps, compressors, and the like used togenerate, store, monitor, regulate, and/or recondition the exemplarydrilling fluid. The drilling fluid may also affect transport or deliveryequipment used to convey the drilling fluid to a well site or downholesuch as, for example, any transport vessels, conduits, pipelines,trucks, tubulars, and/or pipes used to compositionally move the drillingfluid from one location to another, any pumps, compressors, or motors(e.g., topside or downhole) used to drive the drilling fluid intomotion, any valves or related joints used to regulate the pressure orflow rate of the drilling fluid, and any sensors (i.e., pressure andtemperature), gauges, and/or combinations thereof, and the like. Thedrilling fluid may also directly or indirectly affect the variousdownhole equipment and tools that may come into contact with thedrilling fluid such as, but not limited to, wellbore casing, wellboreliner, completion string, insert strings, drill string, coiled tubing,slickline, wireline, drill pipe, drill collars, mud motors, downholemotors and/or pumps, spacer fluid pumps, surface-mounted motors and/orpumps, centralizers, turbolizers, scratchers, floats (e.g., shoes,collars, valves, etc.), logging tools and related telemetry equipment,actuators (e.g., electromechanical devices, hydromechanical devices,etc.), sliding sleeves, production sleeves, plugs, screens, filters,flow control devices (e.g., inflow control devices, autonomous inflowcontrol devices, outflow control devices, etc.), couplings (e.g.,electro-hydraulic wet connect, dry connect, inductive coupler, etc.),control lines (e.g., electrical, fiber optic, hydraulic, etc.),surveillance lines, drill bits and reamers, sensors or distributedsensors, downhole heat exchangers, valves and corresponding actuationdevices, tool seals, packers, cement plugs, bridge plugs, and otherwellbore isolation devices, or components, and the like.

Spacing Fluids Spacer fluids, including those formulated and/or modifiedaccording to the teachings of the present disclosure, may directly orindirectly affect one or more components or pieces of equipmentassociated with the preparation, delivery, recapture, reuse, recycling,and/or disposal of the disclosed spacer fluid. For example, the spacerfluid may affect one or more mixers, related mixing equipment, mud pits,storage facilities or units, composition separators, heat exchangers,sensors, gauges, pumps, compressors, and the like used to generate,store, monitor, regulate, and/or recondition the exemplary spacer fluid.The spacer fluid may also affect any transport or delivery equipmentused to convey the spacer fluid to a well site or downhole such as, forexample, any transport vessels, conduits, pipelines, trucks, tubulars,and/or pipes used to compositionally move the spacer fluid from onelocation to another, any pumps, compressors, or motors (e.g., topside ordownhole) used to drive the spacer fluid into motion, any valves orrelated joints used to regulate the pressure or flow rate of the spacerfluid, and any sensors (i.e., pressure and temperature), gauges, and/orcombinations thereof, and the like. The spacer fluid may also affect thevarious downhole equipment and tools that may come into contact with thespacer fluid such as, but not limited to, wellbore casing, wellboreliner, completion string, insert strings, drill string, coiled tubing,slickline, wireline, drill pipe, drill collars, mud motors, downholemotors and/or pumps, spacer fluid pumps, surface-mounted motors and/orpumps, centralizers, turbolizers, scratchers, floats (e.g., shoes,collars, and valves), logging tools and related telemetry equipment,actuators (e.g., electromechanical devices, and hydromechanicaldevices), sliding sleeves, production sleeves, plugs, screens, filters,flow control devices (e.g., inflow control devices, autonomous inflowcontrol devices, and outflow control devices), couplings (e.g.,electro-hydraulic wet connect, dry connect, and inductive coupler),control lines (e.g., electrical, fiber optic, and hydraulic),surveillance lines, drill bits and reamers, sensors or distributedsensors, downhole heat exchangers, valves and corresponding actuationdevices, tool seals, packers, cement plugs, bridge plugs, and otherwellbore isolation devices, or components, and the like.

As shown in FIG. 13, spacer fluid 80 may be used to flush drilling fluidfrom a subterranean formation 20 in accordance with example embodiments.As illustrated, wellbore 22 may be drilled into formation 20. Whilewellbore 22 is shown extending generally vertically into formation 20,the principles described herein are also applicable to wellbores thatextend at an angle through formation 20, such as horizontal and slantedwellbores. One or more additional conduits (e.g., intermediate casing,production casing, and liners) shown here as casing 30 may also bedisposed in the wellbore 22. Wellbore annulus 32 may be formed by casing30 and walls 24 of wellbore 22. One or more centralizers 34 may beattached to casing 30, for example, to centralize casing 30 in wellbore22 prior to and after flushing of the drilling fluid with the spacerfluid. Spacer fluid 80 may be pumped down the interior of casing 30,through casing shoe 42 at the bottom of casing 30 and up around casing30 into wellbore annulus 32. Other techniques, such as reversecirculation, may also be to introduce spacer fluid 80 into wellbore 22.Spacer fluid 80 may fully displace any drilling fluid remaining inwellbore 22, or may itself be displaced when a cement is introduced intowellbore 22. At least a portion of spacer fluid 80 may exit wellboreannulus 32 via a flow line and be deposited, for example, in one or moreretention pits (not expressly shown). While FIG. 13 generally depicts aland-based drilling assembly, the principles described herein areequally applicable to subsea drilling operations that employ floating orsea-based platforms and rigs, without departing from the scope of thedisclosure,

Fracturing Fluids

During well stimulation treatments, a fracturing fluid with a viscositysufficient to suspend proppant particles and to place the proppantparticles in fractures, may be used to maintain the integrity offractures once the hydraulic pressure creating the fractures isreleased. After the proppant is placed in a fracture and pumping stops,the fracture may remain open instead of closing. Once at least onefracture is created and the proppant is substantially in place, theviscosity of the fracturing fluid usually is reduced by breaking theviscosified treatment fluid via function of a breaking agent, therebydepositing the proppant and allowing the fluid to be recovered from theformation. Fracturing, fluids may provide for proppant delivery withoutbreaking. The proppant delivery fluid may be placed in a wellboresimilar to the methods described above in FIGS. 1 and 13.

Embodiments disclosed herein include:

A. A composite fluid that includes a foundation fluid having animpedance at a frequency, and an additive combined with the foundationfluid that results in a composite fluid having an impedance differentthan the impedance of the foundation fluid at the frequency.

B. A method for creating a composite fluid that includes providing afoundation fluid having an impedance at a frequency, and adding anadditive to the foundation fluid that results in a composite fluidhaving an impedance different than the impedance of the foundation fluidat the frequency.

C. A composite fluid that includes a foundation fluid having a magneticpermeability, and an additive combined with the foundation fluid thatresults in a composite fluid having a magnetic permeability greater thanthe foundation fluid.

D. A method of drilling a wellbore that includes forming a wellbore in aformation with a drill bit attached to a drill string; and pumping adrilling fluid through the drill string, the drill bit and the wellbore,the drilling fluid comprising a foundation fluid having an impedance ata frequency; and an additive combined with the foundation fluid thatresults in a composite fluid having an impedance different than theimpedance of the foundation fluid at the frequency.

Each of embodiments A, B, C, and D may have one or more of the followingadditional elements in any combination: Element 1: wherein the additivecomprises a plurality of particles having a dielectric constant greaterthan a dielectric constant of the foundation fluid that results in thecomposite fluid having a dielectric constant greater than the dielectricconstant of the foundation fluid. Element 2: wherein the additivefurther comprises a conductive fluid soluble in the foundation fluid,the conductive fluid having an electrical conductivity greater than anelectrical conductivity of the foundation fluid that results in thecomposite fluid including the conductive fluid having a dielectricconstant greater than the dielectric constant of the foundation fluid.Element 3: wherein the additive comprises a plurality of particleshaving electric dipoles that results in the composite fluid having adielectric constant greater than a dielectric constant of the foundationfluid. Element 4: wherein the additive comprises a plurality ofparticles having a magnetic permeability greater than a magneticpermeability of the foundation fluid that results in the composite fluidhaving a magnetic permeability greater than the magnetic permeability ofthe foundation fluid. Element 5: wherein the additive comprises aplurality of particles having magnetic dipoles that results in thecomposite fluid having a magnetic permeability greater than a magneticpermeability of the foundation fluid. Element 6: wherein the additivecomprises additional foundation fluid that results in the compositefluid having a dielectric constant or a magnetic permeability less thana dielectric constant or a magnetic permeability of the foundationfluid. Element 7: wherein the composite fluid has a dielectric constantand a magnetic permeability different than that of the foundation fluid.Element 8: wherein the composite fluid has a dielectric constant and amagnetic permeability different than a dielectric constant and amagnetic permeability of the foundation fluid. Element 9: wherein theadditive comprises a plurality of particles having a magneticpermeability greater than the magnetic permeability of the foundationfluid. Element 10: wherein the additive comprises a plurality ofparticles having magnetic dipoles. Element 11: wherein the additiveresults in the composite fluid having a dielectric constant differentthan a dielectric constant of the foundation fluid. Element 12: whereinthe additive results in the composite fluid having a magneticpermeability different than a magnetic permeability of the foundationfluid. Element 13: wherein the additive results in the composite fluidhaving an impedance approximately matching an impedance of the formationnear the drill bit.

Therefore, the disclosed systems and methods are well adapted to attainthe ends and advantages mentioned as well as those that are inherenttherein. The particular embodiments disclosed above are illustrativeonly, as the teachings of the present disclosure may be modified andpracticed in different but equivalent manners apparent to those skilledin the art having the benefit of the teachings herein. Furthermore, nolimitations are intended to the details of construction or design hereinshown, other than as described in the claims below. It is thereforeevident that the particular illustrative embodiments disclosed above maybe altered, combined, or modified and all such variations are consideredwithin the scope of the present disclosure. The systems and methodsillustratively disclosed herein may suitably be practiced in the absenceof any element that is not specifically disclosed herein and/or anyoptional element disclosed herein.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the following claims. As anexample, the teachings of the present disclosure may be applied to anydownhole fluid used for any purpose related to the completion,production, and operation of a wellbore, in addition to fluidsgenerally, such as those used in audio equipment, electromagneticactuators, and biological applications

What is claimed is:
 1. A composite fluid, comprising: a foundation fluidhaving an impedance at a frequency; and an additive combined with thefoundation fluid that results in a composite fluid having an impedancedifferent than the impedance of the foundation fluid at the frequency.2. The composite fluid of claim 1, wherein the additive comprises aplurality of particles having a dielectric constant greater than adielectric constant of the foundation fluid that results in thecomposite fluid having a dielectric constant greater than the dielectricconstant of the foundation fluid.
 3. The composite fluid of claim 2,wherein the additive further comprises a conductive fluid soluble in thefoundation fluid, the conductive fluid having an electrical conductivitygreater than an electrical conductivity of the foundation fluid thatresults in the composite fluid including the conductive fluid having adielectric constant greater than the dielectric constant of thefoundation fluid.
 4. The composite fluid of claim 1, wherein theadditive comprises a plurality of particles having electric dipoles thatresults in the composite fluid having a dielectric constant greater thana dielectric constant of the foundation fluid.
 5. The composite fluid ofclaim 1, wherein the additive comprises a plurality of particles havinga magnetic permeability greater than a magnetic permeability of thefoundation fluid that results in the composite fluid having a magneticpermeability greater than the magnetic permeability of the foundationfluid.
 6. The composite fluid of claim 1, wherein the additive comprisesa plurality of particles having magnetic dipoles that results in thecomposite fluid having a magnetic permeability greater than a magneticpermeability of the foundation fluid.
 7. The composite fluid of claim 1,wherein the additive comprises additional foundation fluid that resultsin the composite fluid having a dielectric constant or a magneticpermeability less than a dielectric constant or a magnetic permeabilityof the foundation fluid.
 8. The composite fluid of claim 1, wherein thecomposite fluid has a dielectric constant and a magnetic permeabilitydifferent than a dielectric constant and a magnetic permeability of thefoundation fluid.
 9. A method for creating a composite fluid,comprising: providing a foundation fluid having an impedance at afrequency; and adding an additive to the foundation fluid that resultsin a composite fluid having an impedance different than the impedance ofthe foundation fluid at the frequency.
 10. The method of claim 9,wherein the additive comprises a plurality of particles having adielectric constant greater than a dielectric constant of the foundationfluid that results in the composite fluid having a dielectric constantgreater than the dielectric constant of the foundation fluid.
 11. Themethod of claim 10, wherein the additive further comprises a conductivefluid soluble in the foundation fluid, the conductive fluid having anelectrical conductivity greater than an electrical conductivity of thefoundation fluid that results in the composite fluid including theconductive fluid including the conductive fluid having a dielectricconstant greater than the dielectric constant of the foundation fluid.12. The method of claim 9, wherein the additive comprises a plurality ofparticles having electric dipoles that results in the composite fluidhaving a dielectric constant greater than a dielectric constant of thefoundation fluid.
 13. The method of claim 9, wherein the additivecomprises a plurality of particles having a magnetic permeabilitygreater than a magnetic permeability of the foundation fluid thatresults in the composite fluid having a magnetic permeability greaterthan the magnetic permeability of the foundation fluid.
 14. The methodof claim 9, wherein the additive comprises a plurality of particleshaving magnetic dipoles that results in the composite fluid having amagnetic permeability greater than a magnetic permeability of thefoundation fluid.
 15. The method of claim 9, wherein the additivecomprises additional foundation fluid, the additional foundation fluidthat results in the composite fluid having a dielectric constant or amagnetic permeability less than a dielectric constant or a magneticpermeability of the foundation fluid.
 16. The method of claim 9, whereinthe composite fluid has a dielectric constant and a magneticpermeability different than a dielectric constant and a magneticpermeability of the foundation fluid.
 17. A composite fluid, comprising:a foundation fluid having a magnetic permeability; and an additivecombined with the foundation fluid that results in a composite fluidhaving a magnetic permeability greater than the foundation fluid. 18.The composite fluid of claim 17, wherein the additive comprises aplurality of particles having a magnetic permeability greater than themagnetic permeability of the foundation fluid.
 19. The composite fluidof claim 17, wherein the additive comprises a plurality of particleshaving magnetic dipoles.
 20. A method of drilling a wellbore,comprising: forming a wellbore in a formation with a drill bit attachedto a drill string; and pumping a drilling fluid through the drillstring, the drill bit and the wellbore, the drilling fluid comprising: afoundation fluid having an impedance at a frequency; and an additivecombined with the foundation fluid that results in a composite fluidhaving an impedance different than the impedance of the foundation fluidat the frequency.
 21. The method of claim 20, wherein the additiveresults in the composite fluid having a dielectric constant differentthan a dielectric constant of the foundation fluid.
 22. The method ofclaim 20, wherein the additive results in the composite fluid having amagnetic permeability different than a magnetic permeability of thefoundation fluid.
 23. The method of claim 20, wherein the additiveresults in the composite fluid having an impedance approximatelymatching an impedance of the formation near the drill bit.